What other OS could you want, especially on ARM? Most alternatives to Linux are a mistake for web hosting at this point in history. As much as I like some of the ideas and features of some of the alternatives, when taken as a whole, Linux is simply the right tool for the job most of the time.

In short, while its cool if they offer other OS options, my confidence certainly is not shaken by them choosing to roll out first with just Linux support. It seems like the only sensible thing, to me, given how good Linux ARM support is.